A number of different types of jacks are available for industrial use, both of the hydraulic and pneumatic type. Generally speaking, the hydraulic jacks are more expensive than the pneumatic jacks, for a number of reasons. However pneumatic jacks are particularly desirable since most shops have readily available pressurized air, and even mobile servicing units usually have pressurized air available.
But regardless of the type of jack, for industrial applications in servicing trucks, aircraft and the like, a number of strict requirements are imposed upon the jacks by necessity. Primary among the requirements are the size requirements for the jack. Quite frequently, when a truck is being serviced, for example, the jack must be positioned between two tandom wheels in order to engage the walking beam or frame structure of the truck. The same is also true for aircraft, in both of which applications the wheels are frequently spaced quite close together. Additionally, it is quite frequent that ground clearance is minimal, thus further restricting the height of the jack.
Both the width and height limitations impress further difficulties upon pneumatic jacks in particular. With hydraulic jacks, it is relatively simple to increase the pressure of the hydraulic fluid. But for pneumatic jacks, the available air pressure in shops and the like is usually restricted, and thus the jack must be capable of operating typically at a pressure of 100-200 psi air pressure.
The first suggestion to overcome the restrictions on air pressure would of course be to increase the size of the piston in the jack, but this would of course necessitate an enlarged cylinder or housing, and as indicated above, height and width restrictions are barriers to increased piston size. As a further result, the amount of piston travel is of course limited by the height of the cylinder, and thus the amount of lift available is restricted.
In order to increase the available piston surface area, it is known to utilize an oval piston and cylinder arrangement which enables a greater psiton area while still maintaining the width and height requirements of the jack.
However a frequent and severe problem among jacks of an oval configuration is that when the jack is in its elevated position, it is quite easy for the piston to become cocked in the cylinder. When this occurs, frequently the cylinder wall is scored and the piston may become damaged as well. This requires disassembly of the jack and repair. Additionally, the damage to the jack and the down time can be expensive.
In the past, only the contact between the piston rod and the gland prevented cocking of the piston, but due to the construction of air jacks, this was frequently inadequate, and cocking of the piston did result.
The present invention provides an effective yet simple means to reduce or eliminate problems encountered when a piston becomes cocked within the cylinder. This is accomplished by providing at least two guide rods or stabilizer rods which are attached to the piston and extend through the cover of the jack. These stabilizer rods provide two to three times the surface area of contact over prior art jacks to prevent the pistons from cocking.
Accordingly, it is a primary object of this invention to provide an improved pneumatic jack which overcomes disadvantages of prior art jacks.
Still another object of this invention is to provide a pneumatic jack having a low, narrow profile and high capacity.
Yet another object of this invention is to provide a pneumatic jack which prevents cocking of the piston in the cylinder.
Still a further object of this invention is to provide a pneumatic jack of durable construction which may be easily serviced.
Yet a further object of this invention is to provide a pneumatic jack having an automatic safety device to prevent the jack from dropping.
A still further object of this invention is to provide a pneumatic jack having stabilizer rods for preventing cocking of the piston in the cylinder.